This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-234085, filed Aug. 20, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a color image processing apparatus applicable to an image forming apparatus that reproduces an object image onto a copying material by using an electrostatic photography process.
Color adjustment in color copiers is a process used for corrections in case the output image does not exactly reproduce the color of the input image (manuscript) or in case color that is different from the input image is intentionally output.
As color adjustment method which have been disclosed up to now, the image data are converted into coordinate data of three attributes that represent the three attributes of color, namely, hue (H), luminosity (L), and chroma (saturation) (C), and after making adjustments by increasing or decreasing the respective attributes on the coordinates of the three attributes, the process is generally returned to the original color space (additive mixtures of three colors based on red, green, and blue, in other words, the three primary colors of colored light) or CMY (subtractive color mixtures based on cyan, magenta, and yellow, in other words, the three primary colors of coloring materials).
However, it is known that by this method, the processing time required to convert the coordinates of the three attributes is very long. Thus, a conversion method in which color space (HSV, etc.) with high correlation to the three attributes can be made with rather simple operation from RGB color space has been contrived. However, the accuracy of the correlation between the HSV color space and the three attributes is not necessarily sufficient.
Apart from this, in the case of color copiers, at the time of color conversion process where the input image data expressed by color space of three primary colors of colored light (RGB) is converted into color space of three primary coloring materials (CMY) and reproduced on the recording media, as means to obtain the parameters of the color conversion, the method in which sample color patches (color sample images) output by the apparatus (copier) itself is read in, and a plurality of colors for the RGB-CMY data group patches are collected, then the coefficients of the conversion polynomials from RGB to CMY are obtained by the least square method is well known.
However, in this operation, at the time the color patches are read in, mechanical accuracy becomes necessary. Furthermore, in order to obtain color conversion parameter with high accuracy, it is desirable to use multi-color color patches. On the other hand, in order to output multi-color patches to a form of specified area, the individual patch sizes must be made small, and contradictory conditions co-exist.
Above case suggests that an even stricter mechanical accuracy is demanded from the patch read-in to the data extraction. For instance, in case priority is given to the accuracy, it becomes necessary to allow ample time for obtaining the color conversion parameters. On the other hand, in order to reduce the processing time, for instance, if the number of color patches is reduced, there is the problem of lowering the color conversion accuracy.
The present invention aims to provide an image processing apparatus which is applicable to color copiers, and which can conduct color adjustment and color conversion at high speed, high accuracy, and low cost.
The present invention provides a color image processing apparatus which executes color conversion processing on an input image data expressed in first color space, and outputs an output image data expressed in second color space, comprising LUT means for storing color conversion LUT data that is referred to at the time of color conversion processing; storing means for storing a first lattice point color coordinates data equivalent to lattice point address of the color conversion LUT data; color tone instruction means for inputting instruction information instructing color tone changes that have been set beforehand in accordance with a specified conditions; color adjustment parameter composition means for composing color adjustment parameters in accordance with the instruction information input from the color tone instruction means; color adjusting means for color adjusting the first lattice point color coordinates data stored in the storage means with the color adjustment parameter composed by the color adjustment parameters composition means, so as to output a second lattice point color coordinates data; unadjusted color conversion means for converting the second lattice point color coordinates data output from the color adjustment means into the second lattice point color coordinates data expressed in the second color space; color conversion LUT renewal means for renewing the color conversion LUT data stored by the LUT means in accordance with the second lattice point color coordinates data converted by the unadjusted color conversion means; and color conversion means for converting the input image data expressed in the first color space to the output image data expressed in the second color space in accordance with the color conversion LUT data renewed by the color conversion LUT renewal means.
The present invention relates to the First Embodiment, and in order to reflect the color adjustment processing to the color conversion LUT parameters used at the time of color conversion processing, it rewrites the color conversion LUT parameters. By doing so, rapid and high accuracy color adjustment processing and color conversion processing can be conducted without causing non-conformities such as spending long processing time by repeating color conversion processing for color adjustment processing as in the past.
Furthermore, the present invention relates to Second and Third Embodiments, and it is a color image processing apparatus which possesses the complementary color conversion means that outputs image data after the correction expressed in the first color space by conducting complementary color conversion on the input image data expressed in the first color space, and the basic color conversion means that outputs the output image data expressed in the second color space by conducting basic color conversion on the image data after the correction expressed in the first color space output by the complementary color conversion means, and which conducts conversion processing on the input image data expressed in the first color space, and outputs the output image data expressed in the second color space.
The present invention makes it possible to conduct high accuracy color conversion by using higher order polynomial approximation in the case of basic color conversion, and fine color adjustments through complementary color conversion and difference color conversion by conducting color conversion processing of at least two stages, that is, basic color conversion and complementary color conversion (and difference color conversion).
By doing so, for instance, it is possible to conduct the generation of basic color conversion parameters at the time shipment is made from the factory, and execute the complementary color conversion parameters and difference color conversion parameters after actual operation with the purpose of absorbing the changes which occur with the elapse of time or absorbing the changes which occur among individual apparatuses. By performing this, a color adjustment which enables the apparatus to absorb the individual differences as well as the changes which occur with the elapse of time, can be made, and a color image processing apparatus that allows stable color adjustment over a long period of time can be provided.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.